[oilpan]: remove the last references to the "heap/Handle.h" include.

This also removes the actual redirecting header file and related files in the Source/heap directory.

R=ager@chromium.org, erik.corry@gmail.com, haraken@chromium.org, oilpan-reviews@chromium.org, tkent@chromium.org, vegorov@chromium.org, zerny@chromium.org
BUG=

Review URL: https://codereview.chromium.org/253413003

git-svn-id: svn://svn.chromium.org/blink/trunk@172567 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Oilpan: Fix crash in content::WebIDBCursorImpl::~WebIDBCursorImpl.

Our assumption is WebIDBCursorImpl objects are destructed before the
WorkerRunLoop for the owner Worker is stopped.

In Oilpan, IDB objects can outlive the runloop. So we explicitly delete
WebIDBCursor owned by IDBCursor on ActiveDOMObject::stop.

BUG=366530

Review URL: https://codereview.chromium.org/257573002

git-svn-id: svn://svn.chromium.org/blink/trunk@172568 bbb929c8-8fbe-4397-9dbb-9b2b20218538